Among methods for analyzing an amount and concentration of impurities such as metals that have adhered to a silicon wafer surface and evaluating a degree of contamination, there exists a method of analysis and evaluation through collecting chemicals.
In methods of analysis and evaluation through collecting chemicals the device and method to be used are determined according to the region of the silicon wafer.
When the front plane flat part of the silicon wafer is analyzed and evaluated a liquid drop automatic scanning device shown in FIGS. 1A and 1B is used.
FIG. 1A shows a top surface view of the liquid drop automatic scanning device, and FIG. 1B shows a perspective view of the liquid drop automatic scanning device.
As shown in FIGS. 1A and 1B the back plane 10a of the silicon wafer 10 is held and at the same time supported so that it can rotate freely by a fastener not shown in the drawings so that it lies on a horizontal position. On the side of the front plane 10a of the silicon wafer 10, a liquid drop supply arm 20 and a liquid drop holder 30 are disposed. The liquid drop holder 30 is fastened to the tip of the liquid drop supply arm 20 through a vacuum. The liquid drop supply arm 20 has a degree of movability to move the liquid drop holder 30 from the center 10c of the silicon wafer 10 in a radius direction A of the wafer 10. Additionally, the height of the liquid drop supply arm 20 is adjusted to a predetermined height and a liquid drop discharge opening 30a of the liquid drop holder 30 is separated from the front plane 10a of the silicon wafer 10 at only a sufficient predetermined distance to retain chemicals 40. With a controller 50 the liquid drop supply arm 20 is drive-controlled, and a rotation drive source of the silicon wafer 10 is drive-controlled at the same time as the liquid drop holder 30 moves in the radius direction A, and thus the silicon wafer 10 rotates. A tank 60 for collecting the chemicals 40 is provided in a location separate from the silicon wafer 10.
FIGS. 2A through 2D explain means for the liquid drop holder 30 to retain the chemicals 40. FIG. 3 shows a perspective view of a cross section of the liquid drop holder 30.
As shown in FIGS. 2A and 2B, liquid drops 41 are supplied into the liquid drop holder 30 via the inside portion of the liquid drop supply arm 20 and are dropped in succession one drop at a time from the liquid drop discharge opening 30a onto the front plane 10a of the silicon wafer 10. Thus the chemicals 40 on the silicon wafer 10 gradually increase. When at last the chemicals 40 increases enough to reach a discharge opening R shown in FIG. 3, it becomes possible to maintain a state in which a front plane tensile force of the chemicals 40 arises and the liquid drop holder 30 causes the chemicals 40 to contact the front plane 10a of the silicon wafer 10 (FIG. 2C).
Then if the liquid drop supply arm 20 is drive-controlled and the liquid drop holder 30 is moved in a radius direction A then the chemicals 40 can be moved together with the liquid drop holder 30 in the same direction A (FIG. 2D).
Next the operation of the liquid drop automatic scanning device of FIGS. 1A and 1B will be explained.
FIG. 4A is a perspective view showing the movement of the liquid drop holder 30 in a radius direction. FIG. 4B shows the trajectory of the center 40c of the chemicals 40 on the silicon wafer 10.
If the state is reached in which the chemicals 40 is maintained by the liquid drop holder 30 as mentioned above, then the liquid drop supply arm 20 is drive-controlled by the controller 50 and thus the liquid drop holder 30 is positioned on the center 10c of the silicon wafer 10. And as shown in the same FIG. 4A, the rotation drive source is drive-controlled by the controller 50 and thus the silicon wafer 10 is rotated at a fixed speed and at the same time the liquid drop supply arm 20 is drive-controlled by the controller 50 and thus the liquid drop holder 30 is moved in a radius direction A at a predetermined speed (for example, a pitch of several mm per rotation). Thus the liquid drop holder 30 rotates relative to the silicon wafer 10 at a predetermined speed in a circumference direction ω of the silicon wafer 10 while moving at a predetermined speed in the radius direction A of the silicon wafer 10. As a result, as shown in FIG. 4B, the chemicals center 40c is scanned on the front plane 10a of the silicon wafer 10 in the circumference direction ω and forms a spiral-shaped trajectory starting from the center 10c of the silicon wafer 10.
FIG. 5A shows the trajectory of the final circuit of the chemicals center 40c. While the chemicals center 40c is scanned from the scan start point S to the scan finish point G, it advances in the radius direction A for a predetermined distance, thus the radius direction positions of the points are different.
FIG. 5B shows chemicals collecting region 42 in which impurities that contact the chemicals 40 on the front plane of the silicon wafer 10 dissolve into the chemicals 40 and the chemicals 40 including the impurities are collected, and a profile of the chemicals non-collecting region 43 outside the chemicals collecting region 42. The chemicals collecting region 42 as shown by the diagonal lines in FIG. 5B forms a shape according to the final circuit of the trajectory shown in FIG. 5A, thus various portions in the circumference direction of the silicon wafer 10 have various lengths in the radius direction.
The chemicals 40 in which impurities are dissolved is carried to the tank 60 and collected into the tank 60 while still being retained by the liquid drop holder 30. By analyzing the chemicals 40 collected in the tank 60 the degree of contamination on the front plane flat part of the silicon wafer 10 can be evaluated.
Next the device for analyzing and evaluating the chamfered part of the silicon wafer 10 will be described.
FIG. 6 shows a manual chemicals collecting device for collecting chemicals manually on the chamfered part (edge part) of the silicon wafer 10.
As shown in FIG. 6 a dedicated jig 70 is attached at the wafer center 10c of the silicon wafer 10 perpendicular to the wafer surface in the length direction. A ship-bottom shaped groove 81 is formed in a container 80 and the chemicals 40 accumulate in this grove 81. The silicon wafer 10 stands perpendicular to the container 80 and the chamfered part 15 is dipped in the chemicals 40. While maintaining the perpendicular state of the silicon wafer 10 the dedicated jig 70 is manually rotated 90 degrees, ¼ of a circuit in the circumference direction of the chamfered part 15 of the silicon wafer 10 contacts the chemicals 40, and the impurities adhered to the chamfered part 15 of this region are dissolved into the chemicals 40. FIG. 11B shows a collecting region 44 of the silicon wafer 10. An operator sets a position at which a notch 17 is formed as 0 degrees, and performs the chemicals collecting operation by verifying by sight that the dedicated jig 70 turns ¼ of a circuit (90 degrees) from the notch position (0 degrees).
The degree of contamination of the chamfered part 15 of the silicon wafer 10 can be evaluated by analyzing the chemicals 40 collected to the container 80. Note that the chemicals collecting operation is performed in a clean room.
The manual chemicals collecting device is disclosed in patent document 1 below.
Additionally in patent documents 2 and 3 below a configuration of an automatic chemicals collecting device is disclosed which comprises a retaining device and a rotating device, and automatically collects chemicals from a chamfered part (edge part) by rotating a silicon wafer 10 with the rotating device while retaining the silicon wafer 10 in a perpendicular state in the same manner as in the manual chemicals collecting device of FIG. 6 with the retaining device.    Patent Document 1: Japanese Patent Application Laid-Open No. 2000-77492    Patent Document 2: Japanese Patent Application Laid-Open No. 10-92889    Patent Document 3: Japanese Patent Application Laid-Open No. 11-204604